The present invention relates to a semiconductor device and a method of manufacturing the same. More specifically, the present invention relates to a technology for reducing leakage current during reverse operation and improving cutoff characteristics.
Heretofore, a semiconductor device has been known in which a P+ type polysilicon region is formed in contact with one main surface of a semiconductor base having an N− type epitaxial region formed on an N+ type silicon carbide substrate. In such a semiconductor device, a heterojunction is formed between the epitaxial region and the polysilicon region, a top metal electrode is formed on the polysilicon region, and a backside metal electrode is formed on the back surface of the silicon carbide substrate. By applying a voltage between the electrodes using the top metal electrode as an anode and the backside metal electrode as a cathode, rectifying behavior is caused to occur at the heterojunction interface. Thus, diode characteristics can be obtained.
Specifically, conduction characteristics corresponding to forward characteristics of a diode are obtained in the case where a positive potential is applied to the anode with the cathode being grounded, and, on the other hand, blocking characteristics corresponding to reverse characteristics of a diode are obtained in the case where a negative potential is applied to the anode. These forward and reverse characteristics show characteristics similar to those of a schottky barrier formed at a junction between a metal electrode and a semiconductor material, and can be arbitrarily adjusted. Accordingly, the semiconductor device has the advantage that it can be adjusted to an optimum breakdown voltage series as needed compared to a diode utilizing a schottky barrier. Moreover, adjusting the impurity density and the conductivity type of the polysilicon region to predetermined conditions makes it possible to obtain very small leakage current characteristics through an operation mechanism essentially different from that of a schottky barrier.